Feasibility of conducting a cohort randomised controlled trial assessing the effectiveness of a nurse-led package of care for knee pain

OBJECTIVE

To evaluate the feasibility of conducting a cohort randomised-controlled trial (RCT) of a nurse-led package of care for knee pain and determine treatment sequence for use in a future trial.

METHODS

Open label, three-arm, single-centre, mixed-methods, feasibility cohort RCT. Adults aged ≥40 years with moderate-to-severe knee pain for ≥3 months were eligible. Participants were randomised into groups A (non-pharmacological treatment first), B (pharmacological treatment first), or group C (usual care). The intervention was delivered over 26-weeks. Outcomes were dropout rate, recruitment rate, intervention fidelity, ability to collect outcome data and treatment acceptability.

RESULTS

Seventeen participants were randomised and enrolled into each of groups A and B (5.2% recruitment rate), and 174 randomised to group C. Participant characteristics at randomisation were comparable across the three arms. COVID-19 paused the study from March-November-2020. Participants enrolled in groups A and B before March-2020 were withdrawn at restart. Of the 20 participants enrolled after restart, 18 completed the study (10% dropout). The nurse reported delivering most aspects of the intervention with high fidelity. Participants viewed the package of care as structured, supportive and holistic, they learnt about self-managing knee pain, and could engage with and follow the non-pharmacological treatment. Most found the non-pharmacological treatment more useful than the pharmacological treatment, preferring to receive it before or alongside analgesia. Many self-reported questionnaires were not fully completed.

CONCLUSIONS

The nurse-led package of care for knee pain was acceptable with low dropout, although the cohort RCT design may not be feasible for a definitive trial.

TRIAL REGISTRATION

clinicaltrials.gov; NCT03670706.

O107 Endotoxaemia rapidly impacts on skeletal muscle mrna expression under conditions of controlled nutrient availability in humans

Introduction

Inflammation induces changes in muscle protein turnover and mass and dampens insulin stimulated glucose disposal and oxidation. Limited information is available regarding the molecular regulation of these events. We determined the acute effects of lipopolysaccharide (LPS) infusion on targeted muscle mRNA expression.

Methods

Seven healthy, males (age 21.9±0.6 yrs, BMI 23.4±1.2 kg.m-2) participated in this ethically approved randomised crossover design study. On 2 occasions separated by >2 weeks, subjects underwent a 4h hyperinsulinaemic euglycaemic clamp combined with a primed mixed amino-acid (6 g.h-1; to create a ‘fed-state’) infusion, immediately following bolus saline (control) or LPS (4 ng.kg-1) infusion. Vastus lateralis muscle biopsies were obtained at baseline, 120 and 240 min. Muscle mRNA expression was measured (191 targets deemed to be representative of insulin sensitivity, carbohydrate and fat metabolism, inflammation, and protein turnover) using microfluidics TaqMan array cards.

Results

Plasma [TNF alpha] was markedly elevated above control following 60 min of LPS infusion (P<0.05) and remained elevated. Following gene filtering (>1.5 fold change in muscle mRNA expression from baseline, P<0.05), Ingenuity Pathway Analysis identified several metabolic functions significantly altered from baseline after 120 and 240 min in control. The magnitude of change in each metabolic function (-log p value) and the size of each gene network was substantially greater after LPS.

Conclusion

Muscle mRNAs respond rapidly to insulin and amino acid infusion in humans, but the magnitude of response was greater in the presence of LPS and may underpin changes in muscle protein and fuel metabolism seen under these conditions.

Take-home message

Endotoxaemia acts rapidly (within 2 to 4 hours) to alter the expression levels of muscle mRNAs known to be intimately involved in the molecular regulation of muscle mass, insulin resistance and fuel oxidation in human volunteers under controlled conditions of insulin and nutrient availability. This may play a role in the changes in muscle metabolism seen under such conditions.

762 FOR OLDER PATIENTS WITH FRAILTY, SIX WEEKS OF ENFORCED IMMOBILITY HAS NO DETRIMENTAL IMPACT ON MUSCLE STRENGTH OR THICKNESS

Introduction

Immobility can lead to rapid reductions in muscle size, strength and function. Understanding these changes could inform interventions to prevent or slow decline. This longitudinal study aimed to assess the extent of muscle changes in older patients admitted with fragility fractures where clinical management was immobilisation (non-weight bearing) of the affected limb for at least 6 weeks.

Method

Handgrip strength (HGS); knee extensor strength(KES); Vastus Lateralis thickness and cross-sectional area at ultrasound (VLMT, VLCSA); and skeletal mass index (SMI; bioimpedance analysis) were measured in the non-injured limb of 50 patients (88% female) aged ≥70. Pre-existing physical frailty meant patients were limited to transfers only while non-weight bearing. Measurements were performed at hospital admission, 1, 3 and 6 weeks. One-way repeated measures ANOVA was used to assess changes in measurements over time. Additionally, baseline measurements in female patients (n = 36) were compared to 11 healthy, non-frail, non-hospitalised females with comparable BMI, aged ≥70, using independent t-tests. Data are mean + SD.

Results

Patient Clinical Frailty Score (median, IQR) was 5 (4–6). At hospital admission, female patients were older (84 ± 7 years vs. 77 ± 6 years, p < 0.05), weaker (HGS of 9.2 ± 4.7 kg vs. 19.9 ± 5.8 kg, p < 0.001; KES 4.5 ± 1.5 kg vs. 7.8 ± 1.3 kg, p < 0.001) and had lower VLMT (1.38 ± 0.47 cm vs. 1.75 ± 0.30 cm, p = 0.02) than non-frail female controls. Six weeks immobility had no temporal effect on any variable: HGS (F(2,51) = 1.04,p = 0.38,n = 27), KES (F(3,45) = 3.22,p = 0.81,n = 16), VLMT (F(3,54) = 2.52,p = 0.07,n = 19), VLCSA (F(3,42) = 0.74,p = 0.53,n = 15) and SMI (F(2,59) = 0.09,p = 0.94,n = 26).

Conclusion

Older patients admitted with fragility fractures were weaker and had lower VLMT compared to healthy, non-frail older people. This, together with the lack of decline in muscle strength and thickness with 6 weeks immobility strongly suggests muscle resilience was attenuated pre-admission, such that immobility had no further detrimental effect. These results differ from muscle changes seen in younger and non-frail cohorts, and warrants assessment of clinical interventions aimed at increasing muscle mass and function specifically in older people with frailty.

East Midlands knee pain multiple randomised controlled trial cohort study: cohort establishment and feasibility study protocol

INTRODUCTION

Knee pain due to osteoarthritis (OA) is a common cause of disability. The UK National Institute for Health and Care Excellence OA guidelines recommend education, exercise and weight loss advice (if overweight) as core interventions before pharmacological adjuncts. However, implementation of these in primary care is often suboptimal. This study aims to develop a complex intervention with non-pharmacological and pharmacological components that can be delivered by nurses. The feasibility and acceptability of the intervention, and feasibility of undertaking a future cohort randomised controlled trial (RCT) will be explored.

METHODS AND ANALYSIS

In phase 1, we will develop a training programme for nurses and evaluate the fidelity and acceptability of the non-pharmacological element of the intervention. Fidelity checklists completed by the nurse will be compared with video analysis of the treatment sessions. Patients and nurses will be interviewed to determine the acceptability of the intervention and explore challenges to intervention delivery. The non-pharmacological component will be modified based on the findings. In phase 2, we will assess the feasibility of conducting a cohort RCT comprising both the pharmacological and modified non-pharmacological components. We will compare three groups: group A will receive the non-pharmacological components delivered before pharmacological components; group B will receive pharmacological components followed by the non-pharmacological components; and group C (control arm) will continue to receive usual care. Study outcomes will be collected at three time points: baseline, 13 and 26 weeks after randomisation. Qualitative interviews will be conducted with a sample of participants from each of the two active intervention arms.

ETHICS AND DISSEMINATION

This protocol was approved by the East Midlands-Derby Research Ethics Committee (18/EM/0288) and registered at ClinicalTrials.gov (protocol v4.0, 10/02/2020). The study will be reported in accordance with the Consolidated Standards of Reporting Trials guidance and standards. The results will be submitted for publication in peer-reviewed academic journals.

TRIAL REGISTRATION NUMBER

NCT03670706.

Impact of sedentarism due to the COVID-19 home confinement on neuromuscular, cardiovascular and metabolic health: Physiological and pathophysiological implications and recommendations for physical and nutritional countermeasures

The COVID-19 pandemic is an unprecedented health crisis as entire populations have been asked to self-isolate and live in home-confinement for several weeks to months, which in itself represents a physiological challenge with significant health risks. This paper describes the impact of sedentarism on the human body at the level of the muscular, cardiovascular, metabolic, endocrine and nervous systems and is based on evidence from several models of inactivity, including bed rest, unilateral limb suspension, and step-reduction. Data form these studies show that muscle wasting occurs rapidly, being detectable within two days of inactivity. This loss of muscle mass is associated with fibre denervation, neuromuscular junction damage and upregulation of protein breakdown, but is mostly explained by the suppression of muscle protein synthesis. Inactivity also affects glucose homeostasis as just few days of step reduction or bed rest, reduce insulin sensitivity, principally in muscle. Additionally, aerobic capacity is impaired at all levels of the O₂ cascade, from the cardiovascular system, including peripheral circulation, to skeletal muscle oxidative function. Positive energy balance during physical inactivity is associated with fat deposition, associated with systemic inflammation and activation of antioxidant defences, exacerbating muscle loss. Importantly, these deleterious effects of inactivity can be diminished by routine exercise practice, but the exercise dose-response relationship is currently unknown. Nevertheless, low to medium-intensity high volume resistive exercise, easily implementable in home-settings, will have positive effects, particularly if combined with a 15-25% reduction in daily energy intake. This combined regimen seems ideal for preserving neuromuscular, metabolic and cardiovascular health.

Investigating musculoskeletal health and wellbeing; a cohort study protocol

Background

In an ageing population, pain, frailty and disability frequently coexist across a wide range of musculoskeletal diagnoses, but their associations remain incompletely understood. The Investigating Musculoskeletal Health and Wellbeing (IMH&W) study aims to measure and characterise the development and progression of pain, frailty and disability, and to identify discrete subgroups and their associations. The survey will form a longitudinal context for nested research, permitting targeted recruitment of participants for qualitative, observational and interventional studies; helping to understand recruitment bias in clinical studies; and providing a source cohort for cohort randomised controlled trials.

Methods

IMH&W will comprise a prospective cohort of 10,000 adults recruited through primary and secondary care, and through non-clinical settings. Data collection will be at baseline, and then through annual follow-ups for 4 years. Questionnaires will address demographic characteristics, pain severity (0–10 Numerical Rating Scale), pain distribution (reported on a body Manikin), pain quality (McGill Pain Questionnaire), central aspects of pain (CAP-Knee), frailty and disability (based on Fried criteria and the FRAIL questionnaire), and fracture risk. Baseline characteristics, progression and associations of frailty, pain and disability will be determined. Discrete subgroups and trajectories will be sought by latent class analysis. Recruitment bias will be explored by comparing participants in nested studies with the eligible IMH&W population.

Discussion

IMH&W will elucidate associations and progression of pain, frailty and disability. It will enable identification of people at risk of poor musculoskeletal health and wellbeing outcomes who might be suitable for specific interventions, and facilitate generalisation and comparison of research outcomes between target populations. The study will benefit from a large sample size and will recruit from diverse regions across the UK. Purposive recruitment will enrich the cohort with people with MSK problems with high representation of elderly and unwell people.

Trial registration

Clinicaltrials.gov NCT03696134. Date of Registration: 04 October 2018.

Evaluating the efficacy of Internet-Based Exercise programme Aimed at Treating knee Osteoarthritis (iBEAT-OA) in the community: a study protocol for a randomised controlled trial

INTRODUCTION

Knee osteoarthritis (OA) is the most common joint disease worldwide. As of today, there are no disease-modifying drugs, but there is evidence that muscle strengthening exercises can substantially reduce pain and improve function in this disorder, and one very well tested physiotherapy protocol is the 'Better Management of Patients with Osteoarthritis' developed in Sweden. Given the high prevalence of knee OA, a potentially cost-effective, digitally delivered approach to treat knee OA should be trialled. This study aims to explore the benefits of iBEAT-OA (Internet-Based Exercise programme Aimed at Treating knee Osteoarthritis) in modulating pain, function and other health-related outcomes in individuals with knee OA.

METHODS AND ANALYSIS

A randomised controlled trial was designed to evaluate the efficacy of a web-based exercise programme in a population with knee OA compared with standard community care provided by general practitioners (GPs) in the UK. We anticipate recruiting participants into equal groups. The intervention group (n=67) will exercise for 20-30 min daily for six consecutive weeks, whereas the control group (n=67) will follow GP-recommended routine care. The participants will be assessed using a Numerical Rating Scale, the Western Ontario and McMaster Universities Osteoarthritis Index, the Arthritis Research UK Musculoskeletal Health Questionnaire, the Pittsburgh Sleep Quality Index, 30 s sit to stand test, timed up and go test, quantitative sensory testing, musculoskeletal ultrasound scan, muscle thickness assessment of the vastus lateralis, and quadriceps muscles force generation during an isokinetic maximum voluntary contraction (MVC). Samples of urine, blood, faeces and synovial fluid will be collected to establish biomarkers associated with changes in pain and sleep patterns in individuals affected with knee OA. Standard parametric regression methods will be used for statistical analysis.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Research Ethics Committee (ref: 18/EM/0154) and the Health Research Authority (protocol no: 18021). The study was registered in June 2018. The results of the trial will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT03545048.

Metabolic phenotype of skeletal muscle in early critical illness

OBJECTIVES

To characterise the sketetal muscle metabolic phenotype during early critical illness.

METHODS

Vastus lateralis muscle biopsies and serum samples (days 1 and 7) were obtained from 63 intensive care patients (59% male, 54.7±18.0 years, Acute Physiology and Chronic Health Evaluation II score 23.5±6.5).

MEASUREMENTS AND MAIN RESULTS

From day 1 to 7, there was a reduction in mitochondrial beta-oxidation enzyme concentrations, mitochondrial biogenesis markers (PGC1α messenger mRNA expression (-27.4CN (95% CI -123.9 to 14.3); n=23; p=0.025) and mitochondrial DNA copy number (-1859CN (IQR -5557-1325); n=35; p=0.032). Intramuscular ATP content was reduced compared tocompared with controls on day 1 (17.7mmol/kg /dry weight (dw) (95% CI 15.3 to 20.0) vs. 21.7 mmol/kg /dw (95% CI 20.4 to 22.9); p<0.001) and decreased over 7 days (-4.8 mmol/kg dw (IQR -8.0-1.2); n=33; p=0.001). In addition, the ratio of phosphorylated:total AMP-K (the bioenergetic sensor) increased (0.52 (IQR -0.09-2.6); n=31; p<0.001). There was an increase in intramuscular phosphocholine (847.2AU (IQR 232.5-1672); n=15; p=0.022), intramuscular tumour necrosis factor receptor 1 (0.66 µg (IQR -0.44-3.33); n=29; p=0.041) and IL-10 (13.6 ng (IQR 3.4-39.0); n=29; p=0.004). Serum adiponectin (10.3 µg (95% CI 6.8 to 13.7); p<0.001) and ghrelin (16.0 ng/mL (IQR -7-100); p=0.028) increased. Network analysis revealed a close and direct relationship between bioenergetic impairment and reduction in muscle mass and between intramuscular inflammation and impaired anabolic signaling. ATP content and muscle mass were unrelated to lipids delivered.

CONCLUSIONS

Decreased mitochondrial biogenesis and dysregulated lipid oxidation contribute to compromised skeletal muscle bioenergetic status. In addition, intramuscular inflammation was associated with impaired anabolic recovery with lipid delivery observed as bioenergetically inert. Future clinical work will focus on these key areas to ameliorate acute skeletal muscle wasting.

TRIAL REGISTRATION NUMBER

NCT01106300.

The skeletal muscle satellite cell response to a single bout of resistance-type exercise is delayed with aging in men

Skeletal muscle satellite cells (SCs) have been shown to be instrumental in the muscle adaptive response to exercise. The present study determines age-related differences in SC content and activation status following a single bout of exercise. Ten young (22 ± 1 years) and 10 elderly (73 ± 1 years) men performed a single bout of resistance-type exercise. Muscle biopsies were collected before and 12, 24, 48, and 72 h after exercise. SC content and activation status were assessed in type I and type II muscle fibers by immunohistochemistry. Myostatin and MyoD protein and messenger RNA (mRNA) expression were determined by Western blotting and rtPCR, respectively. In response to exercise, it took 48 h (young) and 72 h (elderly) for type II muscle fiber SC content to exceed baseline values (P < 0.01). The number of myostatin + SC in type I and II muscle fibers was significantly reduced after 12, 24, and 48 h of post-exercise recovery in both groups (P < 0.01), with a greater reduction observed at 24 and 48 h in the young compared with that in the elderly men (P < 0.01). In conclusion, the increase in type II muscle fiber SC content during post-exercise recovery is delayed with aging and is accompanied by a blunted SC activation response.

Acute dietary protein intake restriction is associated with changes in myostatin expression after a single bout of resistance exercise in healthy young men

Skeletal muscle satellite cells (SCs) play an important role in the myogenic adaptive response to exercise. It remains to be established whether nutrition plays a role in SC activation in response to exercise. In the present study, we assessed whether dietary protein alters the SC response to a single bout of resistance exercise. Twenty healthy young (aged 21 ± 2 y) males were randomly assigned to consume a 4-d controlled diet that provided either 1.2 g protein ⋅ kg body weight(-1) ⋅ d(-1) [normal protein diet (NPD)] or 0.1 g protein ⋅ kg body weight(-1) ⋅ d(-1) [low protein diet (LPD)]. On the second day of the controlled diet, participants performed a single bout of resistance exercise. Muscle biopsies from the vastus lateralis were collected before and after 12, 24, 48, and 72 h of post-exercise recovery. SC content and activation status were determined using immunohistochemistry. Protein and mRNA expression were determined using Western blotting and reverse transcription polymerase chain reaction. The number of myostatin + SCs decreased significantly at 12, 24, and 48 h (range, -14 to -49%; P < 0.05) after exercise cessation, with no differences between groups. Although the number of myostatin + SCs returned to baseline in the type II fibers on the NPD after 72 h of recovery, the number remained low on the LPD. At the 48 and 72 h time points, myostatin protein expression was elevated (86 ± 26% and 88 ± 29%, respectively) on the NPD (P < 0.05), whereas it was reduced at 72 h (-36 ± 12% compared with baseline) in the LPD group (P < 0.05). This study demonstrates that dietary protein intake does not modulate the post-exercise increase in SC content but modifies myostatin expression in skeletal muscle tissue. This trial was registered at clinicaltrials.gov as NCT01220037.

Skeletal muscle molecular responses to resistance training and dietary supplementation in COPD

BACKGROUND

Skeletal muscle dysfunction is a systemic feature of chronic obstructive pulmonary disease (COPD), contributing to morbidity and mortality. Physical training improves muscle mass and function in COPD, but the molecular regulation therein is poorly understood.

METHODS

Candidate genes and proteins regulating muscle protein breakdown (ubiquitin proteasome pathway), muscle protein synthesis (phosphatidylinositol 3 kinase/Akt/mammalian target of rapamycin pathway), myogenesis (MyoD, myogenin and myostatin) and transcription (FOXO1, FOXO3 and RUNX1) were determined in quadriceps muscle samples taken at four time points over 8 weeks of knee extensor resistance training (RT) in patients with COPD and healthy controls (HCs). Patients with COPD were randomly allocated to receive protein/carbohydrate or placebo supplements during RT.

RESULTS

59 patients with COPD (mean (SD) age 68.0 (9.3) years, forced expiratory volume in 1 s (FEV1) 46.9 (17.8) % predicted) and 21 HCs (66.1 (4.8) years, 105.0 (21.6) % predicted) were enrolled. RT increased lean mass (~5%) and strength (~20%) in all groups. Absolute work done during RT was lower throughout in patients with COPD compared with HCs. RT resulted in increases (from basal) in catabolic, anabolic, myogenic and transcription factor protein expression at 24 h, 4 weeks and 8 weeks of exercise in HCs. This response was blunted in patients with COPD, except for myogenic signalling, which was similar. Nutritional supplementation did not augment functional or molecular responses to RT.

CONCLUSIONS

The potential for muscle rehabilitation in response to RT is preserved in COPD. Except for markers of myogenesis, molecular responses to RT are not tightly coupled to lean mass gains but reflect the lower work done during RT, suggesting some caution when identifying molecular targets for intervention. Increasing post-exercise protein and carbohydrate intake is not a prerequisite for a normal training response in COPD.

Effect of whey protein- and carbohydrate-enriched diet on glycogen resynthesis during the first 48 h after a soccer game

The effect of a whey protein- and carbohydrate (CHO)-enriched diet on the rate of muscle glycogen resynthesis after a soccer match was examined. Sixteen elite soccer players were randomly assigned to a group ingesting a diet rich in carbohydrates and whey protein [CHO, protein, and fat content was 71, 21, and 8E%, respectively; high content of carbohydrates and whey protein (HCP), n = 9] or a group ingesting a normal diet (55, 18, and 26E%; control [CON], n = 7) during a 48-h recovery period after a soccer match. CON and three additional players carried out a 90- and 60-min simulated match without body contacts (SIM90 and SIM60). Muscle glycogen was lowered (P < 0.05) by 54, 48, 53, and 38% after the matches in CON, HCP, SIM90, and SIM60, respectively. Glycogen resynthesis during the first 48 h after the match was not different between CON and HCP, whereas glycogen resynthesis was slower (P < 0.05) during the first 24 h after SIM60 than SIM90 (2.88 ± 0.84 vs 4.32 ± 0.54 mmol/kg dw/h). In HCP, glycogen content in type II muscle fibers was still lowered 48 h after the match. In conclusion, glycogen resynthesis 48 h after a soccer match is not elevated by ingestion of a HCP diet. Furthermore, glycogen resynthesis does not appear to be impaired by body contacts during a match.

Resistance exercise training improves age-related declines in leg vascular conductance and rejuvenates acute leg blood flow responses to feeding and exercise

One manifestation of age-related declines in vascular function is reduced peripheral (limb) blood flow and vascular conduction at rest and in response to vasodilatory stimuli such as exercise and feeding. Since, even in older age, resistance exercise training (RET) represents an efficacious strategy for increasing muscle mass and function, we hypothesized that likewise RET would improve age-related declines in leg blood flow (LBF) and vascular conductance (LVC). We studied three mixed-sex age groups (young: 18-28 yr, n = 14; middle aged: 45-55 yr, n = 20; older: 65-75 yr, n = 17) before and after 20 wk of whole body RET in the postabsorptive state (BASAL) and after unilateral leg extensions (6 × 8 repetitions; 75% 1 repetition maximum) followed by intermittent mixed-nutrient liquid feeds (∼6.5 kJ·kg(-1)·30 min(-1)), which allowed us to discern the acute effects of feeding (nonexercised leg; FED) and exercise plus feeding (exercised leg; FEDEX) on vascular function. We measured LBF using Doppler ultrasound and recorded mean arterial pressure (MAP) to calculate LVC. Our results reveal that although neither age nor RET influenced BASAL LBF, age-related declines in LBF responses to FED were eradicated by RET. Moreover, increases in LBF after FEDEX, which occurred only in young and middle-aged groups before RET (+73 ± 9%, and +90 ± 13%, P < 0.001, respectively), increased in all groups after RET (young +78 ± 10%, middle-aged +96 ± 15%, older +80 ± 19%, P < 0.001). Finally, RET robustly improved LVC under FASTED, FED, and FEDEX conditions in the older group. These data provide novel information that supports the premise that RET represents a valuable strategy to counter age-related impairments in LBF/LVC.

Branched-chain amino acids as fuels and anabolic signals in human muscle

During exercise, there is an increase in amino acid (AA) oxidation accompanied by a depression in whole-body protein synthesis and an increase in protein breakdown. Leucine oxidation increases in proportion to energy expenditure, but the total contribution of BCAA to fuel provision during exercise is minor and insufficient to increase dietary protein requirements. When investigating the effects of AA on the control of muscle protein synthesis (MPS), we showed that increased availability of mixed AAs caused a rise in human MPS to about the same extent as complete meals. Leucine alone (and to some extent other essential, but not nonessential, AAs) can stimulate MPS for a short period, suggesting that leucine acts as a signal as well as a substrate. MPS stimulation by infused AAs shows tachyphylaxis, returning to basal rates after 2 h, possibly explaining why chronically elevated leucine delivery does not elevate MPS clinically. Increased availability of essential amino acids (EAAs) results in dose-related responses of MPS, but, in elderly subjects, there is blunted sensitivity and responsiveness associated with decreased total RNA and mRNA for signaling proteins and signaling activity. Increases of MPS due to EAAs are associated with elevation of signaling activity in the mammalian target of rapamycin (mTOR)/p70 ribosomal subunit S6 kinase eukaryotic initiation factor 4 binding protein 1 pathway, without requiring rises of plasma insulin availability above 10 microU/mL. However, at insulin of <5 microU/mL, AAs appear to stimulate MPS without increasing mTOR signaling. Further increasing availability of insulin to postprandial values increases signaling activity, but has no further effect on MPS.

Phosphocreatine degradation in type I and type II muscle fibres during submaximal exercise in man: effect of carbohydrate ingestion

1. The aim of this study was to examine the effect of carbohydrate (CHO) ingestion on changes in ATP and phosphocreatine (PCr) concentrations in different muscle fibre types during prolonged running and relate those changes to the degree of glycogen depletion. 2. Five male subjects performed two runs at 70 % maximum oxygen uptake (.V(O2,max)), 1 week apart. Each subject ingested 8 ml (kg body mass (BM))(-1) of either a placebo (Con trial) or a 5.5 % CHO solution (CHO trial) immediately before each run and 2 ml (kg BM)(-1) every 20 min thereafter. In the Con trial, the subjects ran to exhaustion (97.0 +/- 6.7 min). In the CHO trial, the run was terminated at the time coinciding with exhaustion in the Con trial. Muscle samples were obtained from the vastus lateralis before and after each trial. 3. Carbohydrate ingestion did not affect ATP concentrations. However, it attenuated the decline in PCr concentration by 46 % in type I fibres (CHO: 20 +/- 8 mmol (kg dry matter (DM))(-1); Con: 34 +/- 6 mmol (kg DM)(-1); P < 0.05) and by 36 % in type II fibres (CHO: 30 +/- 5 mmol (kg DM)(-1); Con: 48 +/- 6 mmol (kg DM)(-1); P < 0.05). 4. A 56 % reduction in glycogen utilisation in type I fibres was observed in CHO compared with Con (117 +/- 39 vs. 240 +/- 32 mmol glucosyl units (kg DM)(-1), respectively; P < 0.01), but no difference was observed in type II fibres. 5. It is proposed that CHO ingestion during exhaustive running attenuates the decline in oxidative ATP resynthesis in type I fibres, as indicated by sparing of both PCr and glycogen breakdown. The CHO-induced sparing of PCr, but not glycogen, in type II fibres may reflect differential recruitment and/or role of PCr between fibre types.

Carbohydrate ingestion prior to exercise augments the exercise-induced activation of the pyruvate dehydrogenase complex in human skeletal muscle

This study examined the effect of pre-exercise carbohydrate (CHO) ingestion on pyruvate dehydrogenase complex (PDC) activation, acetyl group availability and substrate level phosphorylation (glycogenolysis and phosphocreatine (PCr) hydrolysis) in human skeletal muscle during the transition from rest to steady-state exercise. Seven male subjects performed two 10 min treadmill runs at 70 % maximum oxygen uptake (VO2,max), 1 week apart. Each subject ingested 8 ml (kg body mass (BM))-1 of either a placebo solution (CON trial) or a 5.5 % CHO solution (CHO trial) 10 min before each run. Muscle biopsy samples were obtained from the vastus lateralis at rest and immediately after each trial. Muscle PDC activity was higher at the end of exercise in the CHO trial compared with the CON trial (1.78+/-0.18 and 1.27+/-0.16 mmol min(-1) (kg wet matter (WM))(-1), respectively; P 0.05) and this was accompanied by lower acetylcarnitine (7.1+/-1.2 and 9.1+/-1.1 mmol kg(-1) (dry matter (DM))(-1) in CHO and CON, respectively; P<0.05) and citrate concentrations (0.73+/-0.05 and 0.91+/-0.10 mmol (kg DM)(-1) in CHO and CON, respectively; P<0.05). No difference was observed between trials in the rates of muscle glycogen and PCr breakdown and lactate accumulation. This is the first study to demonstrate that CHO ingestion prior to exercise augments the exercise-induced activation of muscle PDC and reduces acetylcarnitine accumulation during the transition from rest to steady-state exercise. However, those changes did not affect the contribution of substrate level phosphorylation to ATP resynthesis.

Contraction-induced muscle fiber damage is increased in soleus muscle of streptozotocin-diabetic rats and is associated with elevated expression of brain-derived neurotrophic factor mRNA in muscle fibers and activated satellite cells

The expression of brain-derived neurotrophic factor (BDNF) is elevated in the soleus muscle of streptozotocin-diabetic rats. To determine whether this diabetes-induced elevation was associated with or enhanced by muscle activity we have induced high-intensity muscle contraction by electrically stimulating the sciatic nerve. In 6-week diabetic rats, intense contraction of the soleus muscle resulted in a two- to four-fold elevation of BDNF mRNA and increased plasma levels of creatine kinase that were associated with severe focal muscle fiber damage and concomitant satellite cell activation. Focal muscle fiber damage and concomitant satellite cell activation were also observed in the soleus muscle of nonstimulated diabetic rats, but to a much lesser extent. No effects of muscle contraction, i.e., experimentally induced or during normal daily activity, on muscle fiber structure or BDNF mRNA expression were seen in diabetic extensor digitorum longus (EDL) muscle. Using a nonradioactive in situ hybridization technique for electron microscopy, the elevated expression of BDNF mRNA in the diabetic soleus muscle was localized within muscle fibers as well as activated satellite cells. This study shows that diabetic soleus muscle, in contrast to diabetic EDL and to soleus and EDL muscle of normal animals, is highly susceptible to contraction-induced damage. Intense contraction and the associated muscle fiber damage in the diabetic soleus muscle result in an upregulation of BDNF mRNA in muscle fibers and activated satellite cells, which may be involved in the restoration and/or maintenance of nerve/muscle integrity.

The effect of dietary creatine supplementation on skeletal muscle metabolism in congestive heart failure

AIMS

To assess the effects of dietary creatine supplementation on skeletal muscle metabolism and endurance in patients with chronic heart failure.

METHODS

A forearm model of muscle metabolism was used, with a cannula inserted retrogradely into an antecubital vein of the dominant forearm. Maximum voluntary contraction was measured using handgrip dynanometry. Subjects performed handgrip exercise, 5 s contraction followed by 5 s rest for 5 min at 25%, 50%, and 75% of maximum voluntary contraction or until exhaustion. Blood was taken at rest and 0 and 2 min after exercise for measurement of lactate and ammonia. After 30 min the procedure was repeated with fixed workloads of 7 kg, 14 kg and 21 kg. Patients were assigned to creatine 20 g daily or matching placebo for 5 days and returned after 6 days for repeat study.

RESULTS

Contractions (median (25th, 75th interquartiles)) until exhaustion at 75% of maximum voluntary contraction increased after creatine treatment (8 (6, 14) vs 14 (8, 17), P = 0.025) with no significant placebo effect. Ammonia per contraction at 75% maximum voluntary contraction (11.6 mumol/l/contraction (8.3, 15.7) vs 8.9 mumol/l/contraction (5.9, 10.8), P = 0.037) and lactate per contraction at 75% maximum voluntary contraction (0.32 mmol/l/contraction (0.28, 0.61) vs 0.27 mmol/l/contraction (0.19, 0.49), P = 0.07) fell after creatine but not after placebo.

CONCLUSIONS

Creatine supplementation in chronic heart failure augments skeletal muscle endurance and attenuates the abnormal skeletal muscle metabolic response to exercise.

Carbohydrate ingestion and single muscle fiber glycogen metabolism during prolonged running in men

The aim of this study was to examine the effect of carbohydrate (CHO) ingestion on glycogen degradation in type I and type II muscle fibers during prolonged running by using a quantitative biochemical method. To this end, eight male subjects ran at 70% maximal oxygen uptake to exhaustion on a motorized treadmill on two occasions, 1 wk apart. On each occasion, the subjects ingested 8 ml/kg body wt of either placebo (Pl) or a 5.5% CHO-electrolyte solution (CHO-E) immediately before the start of the run and 2 ml/kg body wt every 20 min thereafter. Needle biopsy samples were obtained from the vastus lateralis muscle before and after each trial and also at the time coinciding with Pl exhaustion in the CHO-E trial. Running time to exhaustion was longer (P < 0.01) in the CHO-E trial compared with the Pl trial (132.4 +/- 12.3 and 104.3 +/- 8.6 min, respectively). A 25% reduction in glycogen utilization in type I fibers only was observed in the CHO-E trial compared with the Pl trial (215.2 +/- 27.5 vs. 285.4 +/- 30.1 mmol/kg dry wt; P < 0.01). Furthermore, in the CHO-E trial, in contrast to the Pl trial, both muscle ATP and phosphocreatine concentrations were well maintained throughout exercise. Therefore, because in both the Pl and CHO-E trials the type I fibers were glycogen depleted at the point of exhaustion (31.6 +/- 10.3 and 28.1 +/- 7.1 mmol/kg dry wt, respectively), it is proposed that CHO ingestion improved endurance capacity by contributing to oxidative ATP production specifically in type I fibers and by doing so delayed the development of glycogen depletion in this fiber type.

Carbohydrate ingestion and glycogen utilization in different muscle fibre types in man

1. The effect of carbohydrate (CHO) ingestion on muscle glycogen utilization during exercise was examined on seven male subjects completing two 60 min treadmill runs at 70% maximum oxygen uptake (VO2,max), 1 week apart. On each occasion the subjects consumed either water or a 5.5% CHO-electrolyte solution immediately before and during exercise. Muscle samples were obtained from the vastus lateralis by needle biopsy before and immediately after exercise. Venous blood samples were also collected from an ante-cubital vein at rest and at 10, 20, 40 and 60 min into the run. 2. Higher blood glucose concentrations (P < 0.01) were observed throughout the run during the CHO trial compared with the water trial. Serum insulin concentration was only higher after 20 min of exercise (P < 0.01). 3. A 28% reduction in mixed glycogen utilization was observed as a result of CHO ingestion when compared with water ingestion (108.7 +/- 16.3 vs. 150.9 +/- 19.9 mmol (kg dry matter)-1, respectively; P < 0.01). 4. The ingestion of the CHO solution resulted in sparing of glycogen in type I (slow twitch) fibres only (38 +/- 7% degradation of glycogen as opposed to 66 +/- 3% during the water trial; P = 0.01).

A comparison of the beta 1-selectivity of conventional metoprolol and metoprolol CR during exercise in healthy volunteers

This paper reports on a randomized double-blind crossover study to compare the effects of daily treatment with 100 mg conventional metoprolol (M100), 50 or 100 mg slow-release metoprolol CR (CR50, CR100) and placebo on the response to treadmill walking exercise in 12 healthy volunteers. Twenty minutes of exercise was undertaken at 1.5 h post-dose (Ex1) and again at 4 h (Ex2). During Ex1 all metoprolol preparations caused a reduction in the exercise-induced increase in heart rate when compared to placebo (P < 0.001). The exercise-induced increase in plasma glycerol, an indicator of lipolysis, was diminished by all metoprolol preparations but to a greater extent by M100 (P < 0.05). Rises in plasma ammonia were used to assess the net degradation of energy-rich adenine nucleotides by skeletal muscle during exercise. When compared to placebo, a significant elevation in plasma ammonia was seen only during exercise with M100 (P < 0.05). The perceived exertion at the end of exercise was also greatest on conventional metoprolol. The differences between the effects of conventional and CR formulations of metoprolol were less when exercise was repeated 4 h post dosing. We conclude that metoprolol CR may offer advantages over the conventional preparation, in subjects regularly engaging in exercise, by reducing the metabolic stress imposed upon skeletal muscle.